Year of Award


Document Type


Degree Type

Master of Science (MS)

Degree Name

Environmental Studies

Department or School/College

Environmental Studies Program

Committee Chair

Len Broberg

Commitee Members

Marcel Huijser, Natalie Dawson


large mammal, highway, crossing structure, fragmentation, road, underpass


University of Montana

Subject Categories

Ecology and Evolutionary Biology | Other Ecology and Evolutionary Biology


In recent decades, there has been an increase of engineering projects that seek to mitigate the barrier effect roads impose on wildlife by installing wildlife crossing structures that promote permeability of the road corridor. The 41 fish and wildlife crossing structures installed along a 90km stretch of US Highway 93 on the Flathead Indian Reservation in western Montana, represent one of the most extensive of such projects in North America. As mitigation efforts are increasingly considered and implemented in road construction projects, the need to assess these structures’ effectiveness grows. This study is the first to compare observations of animal movement rates at structures to expected frequencies estimated from observations using the same sampling methodology, within the same time-step, and in contiguously adjacent habitat. I investigated performance measures of wildlife use for 15 congruent crossing structures installed on US Highway 93 on the Flathead Indian Reservation between Evaro and Polson, Montana for one field season between April and November 2015. Across all structures studies, large mammals were 2.6 times more likely to use crossing structures. As groups, deer and carnivores were 2.7 and 1.7 times as likely to use structures on average, respectively. Despite significantly positive corridor-wide performance, differentials for individual crossing structures varied considerably from -1.15 to 6.46 average movements per day. This highlights the importance of using many congruent structures as replicates to determine performance measures. This study illustrates an efficient and rigorous methodology for rapidly assessing the performance of wildlife crossing structures that can be applied to mitigation projects at any scale.

Thesis_Andis_SupplementalMaterials.pdf (1291 kB)
Supplemental maps



© Copyright 2016 Adam Andis